The flash flood warning in Nepal came far too late for many people
The flash flood, triggered by a mountain landslide and glacier collapse in the Himalayas, surged at speeds of up to 190 kilometres per hour, wiping out entire villages. “The warning from the authorities arrived only about half an hour after the collapse, and even then, it reached only a portion of the population at risk,” says glaciologist Pascal Egli of NTNU.
At least 1,455 people are confirmed dead following the flood disaster in Nepal on 26 August. Over 5,000 more are missing. Fourteen power stations and 38 schools were completely or partially destroyed, while 68 bridges and 42 kilometres of roadway were washed away.
Staggering scale
“The scale of the tragedy is immense and overwhelming. This is likely the greatest disaster we have seen in the Himalayas in decades. The videos we have seen show that this is a type of event that is extremely difficult to predict or issue warnings for,” says Pascal Emanuel Egli, a glaciologist and associate professor at NTNU.
Egli is an expert in geophysics and glacier hydrology. He works on numerous international projects concerning natural hazards and water resources related to permafrost, snowmelt, and glaciers.
Researcher friend lost his entire village
A village was located within the circled area. Photo/Illustration: Sunil Tamang
Egli monitored the disaster in Nepal closely after the tragedy. Updates from international research colleagues arrived in his inbox several times an hour: analyses, seismic data, new satellite photos, aerial and drone imagery, and data logs from whatever monitoring equipment remains along the riverbed.
The NTNU researcher has conducted fieldwork in the region on several occasions. He has also visited the area in Nepal that has been hardest hit.
A friend and fellow researcher, who currently works abroad, is from a village that has been completely wiped out by the mudflow (pictured).
20 kilometres in seven minutes
On Wednesday 26 August, at 08:37, the disaster began at an altitude of over 5,000 metres in the Rasuwa region, along the border between Nepal and Chinese-controlled Tibet. According to Egli, the event was likely triggered when the mountain slope next to the glacier collapsed, taking part of the glacier with it.
Pascal Egli, NTNU
A massive block of the glacier terminus collapsed and fell hundreds of metres straight down. The debris then surged onward and into the Trishuli River at breakneck speed.
“The flash flood raced 20 kilometres down the river course in the first seven minutes. The warning from the authorities arrived at 9am, 23 minutes after the glacier collapse. Approximately 623,000 people received an SMS alert about the approaching disaster.
“By then, it was far too late for many of them. The warning only reached people living furthest downstream,” says Egli.
What role did the glacier play?
The massive landslide was initially registered as an earthquake. Between 100 and 250 million cubic metres of rock, ice, and soil were set in motion. Together, they formed a wall of debris that moved at up to 170–190 kilometres per hour at its peak speed, smashing everything in its path.
“Experts are currently debating what actually triggered the disaster. The landslide itself was massive. Geological factors may be to blame. But the question also remains as to what role the glacier played,” says the NTNU researcher.
Glaciers melt, natural hazards arise
Egli has conducted fieldwork on alpine glaciers in Norway, Switzerland, Chile, Pakistan, India, and Nepal. He currently leads NTNU’s contribution to the major EU project CryoSCOPE (CRYOsphere Science Concluding in new Observations and Productive Exploitation). Researchers from nine countries and twenty research institutions are investigating the impact of climate change on hydrology, on snow and retreating glaciers, and on the natural hazards that can arise as a result.
- Read more: The glaciers’ warning
Mountain lost its structural support
Egli explains that the Himalayan glacier in question has been retreating for years due to climate change. Part of the mountainside had been supported by the glacier for thousands of years. As the glacier melts, that support for the mountain is disappearing.
“In addition, large quantities of meltwater may have exacerbated the instability already present in the mountain.”
The third factor is permafrost, which acts much like a glue holding the rock mass together. As temperatures rise, the permafrost degrades. According to Egli, this can also reduce the mountain’s stability.
Maps and satellite images of the area show that the landslide originated at an altitude of over 5,000 metres. It cascaded down to 3,800 metres and continued toward the Lhende River. An area of nearly 2.3 square kilometres collapsed. Illustration: Screenshot from the report “BHOTEKOSHI–TRISHULI CATASTROPHIC FLOOD.”
Climate and natural hazards
Drawing on field studies from Norway and Switzerland, Egli’s CryoSCOPE group aims to contribute further knowledge regarding glacial hydrology – specifically water flow from melting glaciers and outburst floods. The latter are also known by the Icelandic term jøkullaup, or Glacier Lake Outburst Floods in English. They originate from lakes formed by glacial ice, meltwater, and precipitation. Glacial lakes can drain in a matter of hours, and these outbursts can cause extensive damage as they surge downstream.
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Climate-driven or geological instability?
It was not an outburst flood that caused this disaster, contrary to what many people had assumed. Egli notes that some researchers believe the event was less about climate impact and more about purely geological instability.
“Others – perhaps the majority of people – believe the timing and massive scale suggest that multiple mechanisms were at play simultaneously. There appears to be a broad consensus that melting and warming have accelerated, destabilizing the mountain massif surrounding the glacier.”
The challenge of early warning
Egli is also launching a project in collaboration with Swiss and Indian colleagues. The project will take place in Ladakh, India, with the aim of establishing a cost-effective system for monitoring and providing early warnings of natural hazards.
“The early warning technology itself often works well. However, the risk of failure increases if the scale of an event is massive. Training the local population on how the systems operate can also be a challenge,” he says.
System collapse
Researchers from Nepalese universities and research institutions raise critical questions in a situation report last updatedon 31 August: “Why did we fail to foresee the risk? Why did our warning system not work? Why were the consequences for lives, livelihoods, and infrastructure so severe? And, most importantly: What could we have done differently to reduce such losses?”
On Tuesday, 1 September, Nepalese authorities reported that the flood disaster had claimed over 1,000 lives, with more than 4,500 people still missing. The number was set to rise. The photo shows a mass burial of flood victims in Gokarna, Kathmandu on the same day. Photo: NTB/EPA
Egli refers to a research forum he is part of, which reveals that while the authorities have some measures in place regarding early warning and monitoring, significant failures exist. A memo seen by Gemini states that “the system is collapsing in several ways”.
Standard SMS alerts about floods and high water levels are sent out but lack concrete advice on what people should do. Responsibility is unevenly distributed among local, regional, and national authorities.
Low trust level in researchers and authorities
Furthermore, people in local communities have little trust in either researchers or the authorities. Many openly admit to having ignored warnings in the past. Some only take action when they see for themselves that “something’s happening in the river”, or when a danger alert comes from someone they trust in the village. Many initiatives intended to improve this situation stall once external funding runs out. Training and technical maintenance are not sustained.
Much remains unknown
Pascal Egli conducting fieldwork at a weather station on a glacier. Photo: Gotheca/NTNU
This region of the Himalayas alone has thousands of glaciers and glacial lakes, raising the question of what lies ahead as the planet warms.
“The number of glacial lakes has increased as glaciers retreat. This is dangerous, but fortunately we know a lot about their locations; almost all of them have been mapped. What we know less about–and need to investigate more–is the stability of the moraines damming these lakes,” Egli says.
NTNU’s glacier expert notes that there is still a lot that we do not know, like how much permafrost the moraine contains. Consequently, we don’t know if or when they might collapse. We also lack information about subglacial lakes, unstable mountain slopes and moraines that could trigger landslides.
Where did all the water come from?
The flash flood in the Himalayas carried between 100 and 250 million cubic metres of rock and ice. According to Egli, one of the mysteries is why such enormous volumes of water were released in such a short time. Why didn’t the water lose momentum when the terrain levelled out after approximately seven kilometres, instead continuing with nearly the same violent force and speed?
He speculates aloud. Perhaps part of the explanation lies in the significant drop in elevation and the fact that the meltwater originated not only from beneath the glacier but also partly from within the mountain itself. On its way down, the mass of rock and ice encountered “dead ice” – remnants of another glacier – and may have melted it.
“But that is just a hypothesis. We still have a lot to figure out.”
Originally published in Norwegian, by Sølvi W. Normannsen – 2 September, 2026
